This invention relates to a cyclone burner and, more particularly, to a cyclone burner provided with telescoping cylinders which can be actuated to vary the cross-sectional area of a fuel nozzle.
Pulverized coal furnaces are well-known. In these devices, fuels, such as coal and coke, are first pulverized into a particulate state, then injected into a combustion chamber and finally ignited and burned to produce heat. The fuel is usually pulverized in a mill and then delivered to the furnace suspended in air. It is common to use the same air to grind the fuel, dry it, transport it to the burner and inject it into the combustion chamber This air is commonly referred to as "primary air".
The amount of primary air used to inject fuel into the combustion chamber has been found to be an important variable to the efficiency at which fuel is ignited and consumed. The amount of primary air circulated through the system is not, however, generally variable due to the requirements of the other parts of the system which also use the primary air. Therefore, the ratio of primary air to fuel which would result in the optimal ignition and combustion efficiency is rarely achieved.
Furnace engineers have traditionally designed furnace systems to achieve near optimal combustion efficiency for high quality fuels at normal loads. Low volatile fuels, however, such as anthracite, anthracite silt and coke, which are not easily ignitable, require a decrease in the primary air-to-fuel ratio for efficient ignition and burning. Further, low load burning requires a decrease in the amount of primary air injected into the combustion chamber to offset the decrease in fuel.
To increase the combustion efficiencies while burning low quality fuel or during periods of low load burning, the cyclone burner was developed. Cyclone burners are provided with an air vent which can carry away some of the primary air once the fuel has been transported to the burner. This decreases the primary air-to-fuel ratio of the mixture being injected into the combustion chamber. A further improvement involves the introduction of a substantial amount of relatively hotter air around the fuel injection nozzle and into the combustion chamber. This so-called "sleeve air" can be controlled to increase the combustion efficiency of the fuel.
A cyclone burner used in connection with sleeve air, however, has been found to be unable to provide optimal combustion efficiencies for low quality fuels since these fuels have less volatile matter than other fuels, and therefore require more time to ignite and a longer time to burn for complete combustion. These combustion conditions require that less primary air be injected into the combustion chamber for efficient combustion.
Another problem with the use of cyclone burners arises during low load burning. When the load is decreased, the flow through the burner is less dense due to the increase in the primary air-to-fuel ratio. As density decreases, flow resistance decreases as well. There is thus less resistance to the flow during low load burning as it passes through the injection nozzle. This reduced resistance results in a pressure drop within the injection nozzle which causes more of the primary air to be pulled away from the air vent and into the injection nozzle to balance the pressure differential. Therefore, the amount of air in the injection nozzle during low load burning actually increases rather than merely staying constant. The presence of this additional air, when taken together with the already high primary air-to-fuel ratio present during low load burning, results in an extremely low combustion efficiency.